Soil thermal parameters are mainly inputs for models of soil heat flux. Mathematical models are important tool for predicting the soil heat and water transfer, depending on some fundamentals of soil physical properties. Soil moisture is one of the soil physical properties that have a great effect on thermal parameters. The aim of the work is to describe the behavior of soil thermal parameters under different values of soil moisture, and is to investigate the effect of some fundamentals of soil

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... hysical properties on thermal parameters. We could describe the relationship between thermal diffusivity and soil moisture by ∩ shaped curve using a quadratic equation and evaluate the efficiency of this equation, statistically. Experimental thermal diffusivity (K exp ) by direct method and mathematical models were measured. Mathematical models were Chung and Horton model ( 1987) (K cal-2 ), the model of Arkhangel'skaya (2004) (K cal-3 ) and the suggested quadratic equation (K cal-1 ). Efficiency of the quadratic equation and mathematical models were estimated using the correlation coefficient (R 2 ), Root Mean Square Error (RMSE), and the Nash-Sutcliffe Efficiency (NSE). The values of R 2 , RMSR and NSE for the quadratic equation were 0.978, 0.24 and 0.95, respectively, for sod-podzolic soil under the study. The quadratic equation is a simple and faster equation for forecasting soil thermal diffusivity.